Patients of chronic renal failure are unavoidably treated by dialysis normally at regular intervals over a prolonged period of time, and pathological conditions of increased plasma phosphate concentrations (4.5 mg/dl or more), i.e., hyperphosphatemia, are often appeared in the patients. Because no direct etiological treatment of hyperphosphatemia has been developed so far, diet therapy to lower phosphate absorption, or as a symptomatic therapy, treatment by oral administration of a medicament for hyperphosphatemia which adsorbs phosphate ions in the digestive tract are generally applied. As medicaments for therapeutic treatment of hyperphosphatemia, aluminum hydroxide gel and precipitated calcium carbonate are commonly used.
International Publication WO95/05184 discloses a method for eliminating phosphate ions in vivo by using a polymer such as polyallylamine, polyethylenimine or other, preferably a cross-linked polymer obtained by using a crosslinking agent such as epichlorohydrin or the like. The publicaition teaches that strongly basic anion exchange resins such as Dowex are not preferred from viewpoints that doses are inevitably high because of their weak adsorbability of phosphate ions and the resins may adsorb salts of bile acids. The publication also teaches that the aforementioned polymers are improved in these points compared to the conventional resins.
Aluminum hydroxide gel used as a medicament for therapeutic treatment of hyperphosphatemia has problems of high daily dosage, and moreover, bad taste, which cause difficulty in administration by a patient. Additionally, aluminum ions, formed by dissociation from the aluminum hydroxide gel in contact with gastric hydrochloric acid, are absorbed from the intestinal tract, and as a result, prolonged administration may sometimes cause precipitation of aluminum in the brain and bones and induces so-called osteopathic aluminosis or encephalopathic aluminosis, microcytic anemia or other. On the other hand, precipitated calcium carbonate used as a medicament for therapeutic treatment of hyperphosphatemia also has a problem that calcium ions formed by dissociation in contact with gastric hydrochloric acid may cause hypercalcemia.
In pathologic conditions of chronic renal failure accompanied by hyperphosphatemia, complications such as iron deficiency anemia, metabolic acidosis or other may often appear in patients. It is well known that administration of aluminum hydroxide gel under these conditions may further deteriorate the anemia. In addition, it is also known that cholestyramine (a preparation comprising a polystyrene-type strongly basic anion exchange resin: "Questran", Bristol Myers Squibb Co.), which is used as a cholesterol depressant that adsorbs bile acids, also adsorbs iron ions and suppresses the iron absorption from the intestinal tract to reduce the iron concentration in blood and tissues and lower the hematocrit level. which advances iron deficiency anemia (Digestive Diseases, Vol. 17, No. 3, p.263-269, 1972; and Clin. Res. Vol. 18, p.38, 1970). In addition, international Publication WO94/27621 discloses a method for binding iron ions by using a polymer having amino groups. Accordingly, if polystyrene resins and acrylic resins having amino groups, per se, are administered, the aforementioned adverse effect (iron deficiency anemia) may possibly be generated.